Objective: Early‐stage breast cancer patients generally receive either a mastectomy or a lumpectomy, either by their own choice or that of their surgeon. Sometimes, there is regret about the decision afterward. To better understand regret about surgical decisions, this study examined 2 possibilities: The first is that women who take a dominant or collaborative role in decision making about the surgery express less regret afterward. The second is that congruence between preferred role and actual role predicts less regret. We also explored whether disease stage moderates the relationship between role congruence and decisional regret. Methods: In a cross‐sectional design, 154 women diagnosed with breast cancer completed a survey assessing decisional role preference and actual decisional role, a measure of post‐decision regret, and a measure of disturbances related to breast cancer treatment. Hierarchical regression was used to investigate prediction of decisional regret. Results: Role congruence, not actual decisional role, was significantly associated with less decisional regret, independent of all the control variables. The interaction between disease stage and role congruence was also significant, showing that mismatch relates to regret only in women with more advanced disease. Conclusions: Our findings suggest that cancer patients could benefit from tailored decision support concerning their decisional role preferences in the complex scenario of medical and personal factors during the surgical decision.